My invention relates to a process for making coupling agents for oxidizing hair dye compositions and, more particularly, to a process for making 4-chloro-2-methyl-5-nitro-phenol.
The derivatives of m-aminophenol have great significance as coupling agents for the red range for use in oxidizing hair dye compositions. Recently new m-aminophenol derivatives have been made which are characterized by a high light fastness and good toxicological properties. This kind of m-aminophenol derivative is described for example in the German Open Patent Application No. 3 524 329. The final preliminary stage compound or primer for making of all compositions named in that application is 4-chloro-2-methyl-5-nitro-phenol of the formula(I): ##STR3## whose manufacture is known from British Patent No. 1 100 219.
The process described there is based on 4-chloro-2-methyl aniline, which is first nitrated and subsequently is converted into the nitrophenol (I) by diazotizing and cooking. More recently it has been found that 4-chloro-2-methyl-aniline can produce bladder cancer. Thus the above-described manufacturing process can no longer be used for the amounts required in the typical chemical engineering process.
The nitration of technically available and very economical 4-chloro-2-methyl-phenol is described in the Literature(Zincke, Liebigs Ann. Chem., Seite 417, 222. That transformation results however in a 4-chloro-2-methyl-6-nitro-phenol which is an isomer of the compound (I).
Another process for making 4-chloro-2-methyl-5-nitro-phenol is described in French Patent No. 2 106 907. There the bis-carbonic acid ester of 4-chloro-2-methyl-phenol is first nitrated and subsequently cleaved by alkaline hydrolysis. Among the disadvantages of this process is the required production of bis-carbonic acid ester, which occurs with phosgene or its derivatives and thus produces a safety problem. Also the yield on nitration is poor. The isomeric product called for by the drastic product conditions requires an additional purification step, after whose performance a yield of only 57% of the theoretical yield is attained.